Ash-containing concrete composition

ABSTRACT

A concrete composition that includes (i) a treated palm oil fuel ash, wherein the treated palm oil fuel ash is the only binder present, (ii) a fine aggregate, (iii) a coarse aggregate, and (iv) an alkali activator containing an aqueous solution of sodium hydroxide and sodium silicate. A cured concrete made from the concrete composition is also disclosed with advantageous compressive strength properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.16/533,014, now U.S. Pat. No. 11,174,202, having a filing date of Aug.6, 2019.

BACKGROUND OF THE DISCLOSURE Technical Field

The present disclosure relates to alkali-activated concrete compositionsthat include palm oil fuel ash, and cured concrete made therefrom.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentdisclosure.

According to guidelines of the Intergovernmental Panel on Climate Change(IPCC) and other agencies of the United Nations, mitigating CO₂emissions is a top priority for combating rising global averagetemperatures. One of the practical and sustainable means to achieve thelimits set for the global average temperature at the UN conference ofparties (COP23) is for the cement industry to lower the production ofPortland cement and to develop an economically- andenvironmentally-friendly substitute. CO₂ is a byproduct produced duringthe production of Portland cement, specifically during the formation ofclinker (intermediate product) using elevated temperatures inside akiln, where calcium carbonate from calcium-rich material is convertedinto lime and CO₂. In fact, in 2015, Portland cement generated around2.8 billion tons of CO₂, equivalent to 8% of the total CO₂ generatedglobally. The high levels of CO₂ emitted from cement production is onlyexpected to worsen as global urbanization and economic developmentincrease with higher demand for new buildings and infrastructure.

Therefore, the cement industry has begun research into energy efficientcementitious materials to replace cements such as ordinary Portlandcement (OPC), encouraged by changes in policy, technology, and newopportunities to raise profits and cut costs through decreasinggreenhouse gas emissions. However, only limited progress has been madeso far.

One type of technology being explored is alkali-activated concrete (AAC)using aluminosilicate binders having pozzolanic behavior, owing in partto the vast aluminosilicate material options. AAC is produced using abinder generated from the reaction between aluminosilicate precursor anda highly alkaline solution, which results in little energy dissipationduring production. Many binding materials have been used in alkaliactivated concretes, such as metakaolin, fly ash, natural pozzolan, andother materials generated from industrial and agricultural activities,such as blast furnace slag and rice husk ash.

Another of these aluminosilicate materials is palm oil fuel ash (POFA),an agricultural waste material produced from the burning of palm fibers,empty fruit bunches and kernel shells. The ash produced after burning ofthese waste materials (POFA) has been historically disposed ofindiscriminately in landfills, causing lost profits and health concernsto nearby inhabitants. Vast volumes of POFA are produced in Malaysia,Thailand and Indonesia. In fact, global palm oil production hasincreased from 15.2 million tons in 1995 to 54 million tons in 2012 andit is expected to grow by more than 25% by 2020 to a global level ofmore than 68 million tons (European Palm Oil Alliance, 2014). Therefore,finding constructive and profitable uses for the major waste byproduct,POFA, remains of interest. However, the use of POFA as a bindingmaterial in cement/mortar has significant challenges. For instance, thechemical composition of POFA is characterized by a high amount of SiO₂(in varying quantities depending on the region and treatment), and lowquantities of Al₂O₃ and CaO, which causes bond formation inadequaciesneeded for high strength, hampering its implementation as a binder.

As a result, many aluminosilicate materials such as palm oil fuel ash(POFA) have been used as a supplementary cementing material (as apartial replacement of cement), but have not been used as the solebinder (complete replacement for cement) in concrete.

In view of the forgoing, one object of the present disclosure is toprovide concrete compositions that contain palm oil fuel ash (POFA), andcured concretes made therefrom with advantageous compressive strengthand durability properties. Such concrete compositions may be made withPOFA as the only binder material, which has the benefit of reducing POFAwaste volumes in landfills, conserving natural materials, and reducingCO₂ emissions and energy consumption required for cement manufacture.

BRIEF SUMMARY OF THE DISCLOSURE

Accordingly, it is one object of the present invention to provideconcrete compositions containing treated palm oil fuel ash as the onlybinder material.

It is another object of the present disclosure to provide curedconcrete, formed from curing the concrete composition, with a highcompressive strength.

These and other objects, which will become apparent during the followingdetailed description, have been achieved by the inventors' discoverythat adequate gradation of a treated palm oil fuel ash binder andaggregate enables the POFA material to be used as a complete replacementfor cement such as OPC.

Thus, the present invention provides:

A concrete composition that includes (i) a treated palm oil fuel ash,wherein the treated palm oil fuel ash is the only binder present, (ii) afine aggregate, (iii) a coarse aggregate, and (iv) an alkali activatorcontaining an aqueous solution of sodium hydroxide and sodium silicate.

In some embodiments, the treated palm oil fuel ash is present in anamount of 20 to 30 wt. %, based on a total weight of the concretecomposition.

In some embodiments, the treated palm oil fuel ash is obtainedsequentially from drying raw palm oil fuel ash at 80 to 120° C., sievingto a particle size of less than 300 μm, a first mechanical ball milling,calcining at 500 to 600° C., and a second mechanical ball milling.

In some embodiments, the treated palm oil fuel ash has a median particlesize (d₅₀) of 0.5 to 2.0 μm.

In some embodiments, the treated palm oil fuel ash contains, asconstituent oxides, 60 to 72 wt. % SiO₂, 4 to 8 wt. % Al₂O₃, 3 to 7 wt.% Fe₂O₃, 3 to 8 wt. % CaO, 1 to 5 wt. % MgO, 3 to 7 wt. % K₂O, 0.2 to0.5 wt. % SO₃, 0.1 to 0.25 wt. % Na₂O, and 1 to 5 wt. % of P₂O₃, eachbased on a total weight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash contains, asconstituent oxides, 66 to 68 wt. % SiO₂, 6 to 7 wt. % Al₂O₃, 5 to 6.5wt. % Fe₂O₃, 5 to 6 wt. % CaO, 2.5 to 3.5 wt. % MgO, 4.5 to 6 wt. % K₂O,0.3 to 0.35 wt. % SO₃, 0.18 to 0.2 wt. % Na₂O, and 3 to 4 wt. % of P₂O₃,each based on a total weight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a loss onignition (LOI) of less 3 wt. %, based on a total weight of the treatedpalm oil fuel ash, and a specific surface area of 1.4 to 1.6 m²/g.

In some embodiments, a weight ratio of a combined weight of the coarseaggregate and the fine aggregate to the treated palm oil fuel ash is 1:1to 2:1.

In some embodiments, the fine aggregate has a fineness modulus of 1.8 to2.1 and a saturated surface dry (SSD) specific gravity of 2.5 to 2.7.

In some embodiments, the coarse aggregate has a saturated surface dry(SSD) specific gravity of 2.4 to 2.6.

In some embodiments, the coarse aggregate has a bimodal particle sizedistribution with a first mode particle size of 4 to 6 mm and secondmode particle size of 2 to 3 mm, and a wherein a weight ratio of coarseaggregate having the first mode particle size to coarse aggregate havingthe second mode particle size is 1:1 to 3:1.

In some embodiments, a weight ratio of the coarse aggregate to the fineaggregate is 1:1 to 2:1.

In some embodiments, the alkali activator is formed from an aqueoussolution of sodium hydroxide having a sodium hydroxide concentration of10 to 14 mol/L.

In some embodiments, a weight ratio of the alkali activator to thetreated palm oil fuel ash is 0.3:1 to 0.7:1

In some embodiments, a weight ratio of sodium silicate to sodiumhydroxide is 1:1 to 3:1

In some embodiments, the concrete composition has weight ratio of waterto the treated palm oil fuel ash of 0.06 to 0.98.

In some embodiments, the concrete composition consists of the treatedpalm oil fuel ash, the coarse aggregate, the fine aggregate, sodiumhydroxide, sodium silicate, and water.

A cured concrete containing the concrete composition in cured form.

In some embodiments, the cured concrete has a 28-day compressivestrength of 33 to 49 MPa.

In some embodiments, the cured concrete has a unit weight of 2200 to2300 kg/m³.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an image of typical palm oil fuel ash (POFA) dumping site nearto palm oil mill;

FIG. 2 is a flowchart for a treatment and production process for makingtreated POFA (TPOFA) used in the concrete composition;

FIG. 3 is an image of raw POFA loaded into an oven for drying;

FIG. 4 is a pictorial view of a mechanical ball mill with two millsoperating simultaneously;

FIG. 5 is an image of ground POFA after oven drying and grinding butbefore heat treatment in a gas-operated furnace, where the POFA has ablack appearance;

FIG. 6 is an image of calcined POFA (after heat treatment in agas-operated furnace), where the POFA has a grey appearance.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all of the embodiments of the disclosure are shown.

Definitions

As used herein, the terms “optional” or “optionally” means that thesubsequently described event(s) can or cannot occur or the subsequentlydescribed component(s) may or may not be present (e.g. 0 wt. %).

The phrase “substantially free”, unless otherwise specified, describes aparticular component being present in an amount of less than about 1 wt.%, preferably less than about 0.5 wt. %, more preferably less than about0.1 wt. %, even more preferably less than about 0.05 wt. %, yet evenmore preferably 0 wt. %, relative to a total weight of the compositionbeing discussed.

The term “comprising” is considered an open-ended term synonymous withterms such as including, containing or having and is used herein todescribe aspects of the invention which may (or may not) includeadditional components, functionality and/or structure. Terms such as“consisting essentially of” are used to identify aspects of theinvention which exclude particular components that are not explicitlyrecited in the claim but would otherwise have a material effect on thebasic and novel properties of the concrete composition in either a dry,wet or cured form. Basic and novel properties of the present disclosureinclude, but are not limited to, the strength such as compressivestrength, curing time, slump, workable flow, and viscosity. The term“consisting of” describes aspects of the invention in which only thosefeatures explicitly recited are included and thus other components notexplicitly or inherently included are excluded.

As used herein, the term “binder” refers to a composition or substancewith one or more constituents that is capable of binding materialstogether, once set. While a “binder” classically refers to materials ormixtures of materials that are “cements” (e.g., Portland cement), in thepresent disclosure, a “binder” may be a cement or any other materialthat is capable of forming cement or capable of forming materials withcement-like binding properties. Therefore, included in the definition of“binder” are those materials that have little to no cementitious valueby themselves but which will, in finely divided form and in the presenceof water, react chemically with certain chemicals present in theconcrete composition to form compounds possessing cementitiousproperties. For example, pozzolans and burned organic matter residues(e.g. fly ash, silica fume from silicon smelting, highly reactivemetakaolin, palm oil fuel ash, date palm ash, etc.), while notconsidered “cements”, are considered to be “binders” in the presentdisclosure.

As used herein, a “concrete composition” refers to a workable mixturecomprising water, aggregate (e.g., coarse and fine aggregate), andbinder, which has not been cured/set/hardened, but which is capable ofbeing cured/set/hardened to form useful building/structural materialssuch as concrete blocks. As used herein, a “cured concrete” refers to acured/set/hardened form of the concrete composition which has formedinto a hard matrix or stone-like material and is distinguished from theconcrete composition in that it is no longer workable.

As used herein, “total aggregate” or “TA” refers to the total amount ofcoarse aggregate and fine aggregate employed in the concrete compositionand cured concrete.

Concrete Compositions

In an effort to reduce CO₂ emissions, the cement industry has turned toreplacing cement binders such as ordinary Portland cement with low costburned agricultural waste products possessing binding properties.However, even when used as a partial cement replacement, such burnedagricultural waste products often impart inadequate strength properties(e.g., compressive strength) to the concrete or mortar, once cured. Suchinadequacies are exacerbated when attempting to completely replacecement with burned agricultural waste products.

Thus, the present disclosure provides a concrete composition(specifically an alkali-activated concrete, AAC) in which the onlybinder present is a treated palm oil fuel ash, and which sets into ahigh compressive strength cured concrete. The concrete compositiongenerally comprises, consists essentially of, or consists of a treatedpalm oil fuel ash as binder, a coarse aggregate, a fine aggregate, analkali activator of sodium hydroxide and sodium silicate, and water. Theconcrete composition may optionally contain one or more additives suchas a strength enhancer, an accelerator, a retarder, a plasticizer (e.g.,a superplasticizer), a pigment, a corrosion inhibitor, a bonding agent,and a reinforcing material.

Palm Oil Fuel Ash (POFA)

The oil palm is a tall-stemmed tree which belongs to the familyArecaceae (commonly known as palms). Oil palm trees, primarily theAfrican oil palm Elaeis guineensis, and to a lesser extent the Americanoil palm Elaeis oleifera and the maripa palm Attalea maripa, arecultivated for their palm oil producing fruit. The countries in theequatorial belt that cultivate oil palm are Benin Republic, Colombia,Ecuador, Nigeria, Zaire, Malaysia, and Indonesia, of which Malaysia isthe largest producer of palm oil and palm oil products (around 47-51% ofthe worlds exports of palm oil). In the palm oil industry, palm oil isextracted from the fruit and copra of the palm oil tree. After theextraction process, waste products such as palm oil fibers, shells, andempty fruit brunches are burned as biomass boiler fuel at 800 to 1,000°C. to boil water, which generates steam to power a turbine for supplyingelectrical energy to the entire palm oil mill extraction process.Usually, the palm oil waste product burned in the boiler is made up ofabout 85% palm oil fibers and about 15% shells and empty fruit bunches,although these percentages may of course vary. The resulting ashy,combustion byproduct is palm oil fuel ash (POFA), which constitutesabout 5 wt. % of solid waste products formed during palm oil processing.POFA does not have sufficient nutrient value to be used as fertilizerand has traditionally been disposed in open fields (profitless).

The inventors have found that palm oil fuel ash, specifically palm oilfuel ash which is treated in a certain way, can be used as a fullreplacement binder for cement in concrete compositions without adverselyaffecting the compressive strength of the cured concrete, when used incombination with an alkali activator.

‘Raw’ palm oil fuel ash, that is, palm oil fuel ash as it isformed/received from the oil palm boiler, typically has too high acarbon content (caused by incomplete burning of the residue) for use asan acceptable binder. Raw POFA typically also has a high moisturecontent of from 3 to 19 wt. %, or 4 to 15 wt. %, or 5 to 10 wt. % water,based on a total weight of the POFA, and a relatively large particlesize, for example a median particle size (d₅₀) of 55 to 75 μm,preferably 60 to 70 μm, preferably 64 to 66 μm.

In preferred embodiments, the palm oil fuel ash utilized herein istreated palm oil fuel ash, which is palm oil fuel ash which has beensubjected to a combination of drying, sieving, ball milling, andcalcining. Briefly, treated palm oil fuel ash may be formed according tothe following procedure.

The raw palm oil fuel ash obtained from a palm oil production facility(e.g., palm oil mill, United Oil Palm Industries Sdn. Bhd. in NibongTebal, Penang, Malaysia) may first be dried, for example, in an oven at80 to 120° C., preferably 90 to 110° C., preferably 95 to 105° C.,preferably about 100° C., to reduce the moisture content to below 5 wt.%, preferably below 4 wt. %, preferably below 3 wt. %, preferably below2 wt. %, preferably below 1 wt. %. The raw palm oil fuel ash may bedried for any amount of time that provides an adequately dried product,typically, for drying times of 12 to 48 hours, preferably 16 to 36hours, preferably 20 to 30 hours, preferably 24 hours.

The resulting dried palm oil fuel ash may then be subjected to sievingthrough one or more sieves of different size, preferably two or moresieves of different size, for example, sequentially through sieves ofdecreasing size to remove coarser and unwanted particulates. Inpreferred embodiments, the dried palm oil fuel ash is sievedsequentially through sieves of decreasing size, preferably through a setof two sieves of decreasing size, to provide sieved POFA having aparticle size of less than 400 μm, preferably less than 350 μm,preferably less than 300 μm. For example, the dried POFA may be sievedsequentially through a set of 600 μm and 300 μm sieves, to providesieved POFA containing no particles above 300 μm. Alternately the POFAmay be sieved immediately upon removal from the kiln or boiler withoutintermediate drying.

The resulting sieved palm oil fuel ash may then be subjected to a firstmechanical ball milling procedure to reduce the particle size and/or toincrease the surface area of the ash. Any type of ball milling apparatusknown to ordinary skill in the art may be employed, including, but notlimited to, a standard ball mill, a planetary mill, a vibration mill, anattritor—stirring ball mill, a pin mill, or a rolling mill. The vialsand balls used for the ball milling may be individually selected fromagate (cryptocrystalline silica), corundum (Al₂O₃), zirconium oxide(ZrO₂), stainless steel (Fe, Cr, Ni), tempered steel (Fe, Cr), andtungsten carbide (WC), preferably stainless steel (e.g., SS 316). Insome embodiments, the balls employed in the ball milling operation havea size of from 6 to 32 mm, preferably 8 to 28 mm, preferably 10 to 24mm, preferably 12 to 20 mm, preferably a variety of ball sizes areemployed for the ball milling operation.

The following ball milling parameters may be utilized. The ball topowder ratio (BPR) or charge ratio represents the weight ratio of themilling balls to the POFA charge. Various BPRs may be employed, buttypically a BPR may range from 1:1 to 10:1, preferably 2:1 to 9:1,preferably 3:1 to 8:1, preferably 4:1 to 7:1, preferably 5:1 to 6:1. Thesieved palm oil fuel ash may be ball milled at a rotational speed of 100to 600 rpm, preferably 120 to 500 rpm, preferably 140 to 400 rpm,preferably 160 to 300 rpm, preferably 180 to 200 rpm. The milling timemay also influence the product morphology and particle size. Suitablemilling times that may be practiced herein range from 15 minutes to 8hours, preferably 30 minutes to 6 hours, preferably 1 to 5 hours,preferably 1.5 to 4.5 hours, preferably about 2 to 4 hours, althoughshorter or longer milling times may also be practiced. Further, thesieved palm oil fuel ash may be ball milled in various atmospheres, forexample, in some embodiments, ball milling is performed in air (or agenerally oxygen-containing atmosphere, e.g., which includes anyatmosphere that contains at least 20%, preferably at least 40%,preferably at least 60%, preferably at least 80%, preferably at least90%, preferably at least 95%, preferably at least 99%, or about 100%oxygen by volume). Alternatively, ball milling may be carried out underan inert atmosphere such as under nitrogen or argon, preferably argon.The resulting product may be referred to herein as ground palm oil fuelash or “GPOFA”. In general, the GPOFA has a median particle size (d₅₀)of 2.8 to 3.5 μm, preferably 2.9 to 3.1 μm, preferably 2.96 to 3.0 μm.

At this stage, GPOFA still contains a relatively high amount of unburnedcarbon, with a loss on ignition (LOI) of greater than 8 wt. %, orgreater than 9 wt. %, or greater than 10 wt. %, and a correspondinglylow amount of constituent oxides useful for enhancing binding properties(see Table 1 for an example chemical constitution of GPOFA). To removethe unburned carbon content and to provide an ash material with improvedpozzolanic properties, the GPOFA is preferably calcined. The calcinationmay be performed in a furnace, for example, a gas-powered furnace. Thecalcination may be performed using a pre-set temperature program orusing other variable temperature systems known by those of ordinaryskill in the art. The GPOFA may be calcined under isothermal conditionsor under variable temperature conditions, typically at a temperaturerange of 400 to 900° C., preferably 425 to 850° C., preferably 450 to800° C., more preferably 475 to 750° C., preferably 500 to 700° C.,preferably 550 to 600° C. The calcination is typically performed for 20minutes to 8 hours, preferably 40 minutes to 6 hours, preferably 60minutes to 4 hours, preferably 80 minutes to 3 hours, preferably 90minutes to 2 hours, although shorter or longer calcination times mayalso be used herein.

While the calcined palm oil fuel ash may possess adequate bindingcapabilities when employed as a partial cement replacement, or in ablend (binary, ternary, etc.) with other binding materials (e.g., flyash, ground blast furnace slag, silica fume, metakaolin, etc.), it hasbeen discovered that subjecting the calcined palm oil fuel ash to asecond mechanical ball billing procedure provides a palm oil fuel ashproduct with the highest performance (referred to herein as treated palmoil fuel ash or “TPOFA”), which enables its use as a full cementreplacement, and without the need for additional binders. The parametersof the second ball milling procedure are as described for the first ballmilling procedure above. The parameters used (the type of equipment, thematerials used for the vials, the materials used for the balls, the ballsize, the BPR, the rotational speed, the milling time, the millingatmosphere) for the first ball milling and the second ball milling maybe the same, or different, preferably the parameters used for the firstand second ball milling operations are the same.

Treated palm oil fuel ash (TPOFA) may vary in terms of the percent ofconstituent oxides present depending on a number of factors, such as thetype of oil palm tree cultivated, the source/location of the oil palmtree cultivated, the relative proportion of the waste products (palm oilfibers, shells, and empty fruit brunches) combusted to produce the POFA,the combustion conditions, as well as the post-combustion processing,etc. The treated palm oil fuel ash used herein generally comprises,consists of, or consists essentially of, SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO,K₂O, SO₃, Na₂O, and P₂O₃. In preferred embodiments, the treated palm oilfuel ash utilized in the present disclosure has a total content of SiO₂,Al₂O₃, and Fe₂O₃ that complies with ASTM C618 class F standards forpozzolan, which is incorporated herein by reference in its entirety. Thepresent disclosure contemplates using a wide variety of treated palm oilfuel ash materials, with the following constitutional makeup beingpreferred.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of SiO₂ of 60 to 72 wt. %, preferably 61 to 71 wt. %,preferably 62 to 70 wt. %, preferably 63 to 69 wt. %, preferably 64 to68 wt. %, preferably 65 to 67.5 wt. %, preferably 66 to 67 wt. %, basedon a total weight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of Al₂O₃ of 4 to 8 wt. %, preferably 4.5 to 7.5 wt. %,preferably 5 to 7 wt. %, preferably 5.5 to 6.8 wt. %, preferably 6 to6.5 wt. %, based on a total weight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of Fe₂O₃ of 3 to 7 wt. %, preferably 3.5 to 6.5 wt. %,preferably 4 to 6.3 wt. %, preferably 4.5 to 6.1 wt. %, preferably 5 to6 wt. %, preferably 5.5 to 5.8 wt. %, based on a total weight of thetreated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of CaO of 3 to 8 wt. %, 3.5 to 7 wt. %, preferably 4 to 6.5wt. %, preferably 4.5 to 6.3 wt. %, preferably 5 to 6.1 wt. %,preferably 5.3 to 6 wt. %, preferably 5.5 to 5.8 wt. %, based on a totalweight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of MgO of 1 to 5 wt. %, preferably 1.5 to 4.5 wt. %,preferably 2 to 4 wt. %, preferably 2.5 to 3.8 wt. %, preferably 3 to3.5 wt. %, preferably 3.1 to 3.2 wt. %, based on a total weight of thetreated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of K₂O of 3 to 7 wt. %, preferably 3.5 to 6.5 wt. %,preferably 4 to 6 wt. %, preferably 4.5 to 5.8 wt. %, preferably 5 to5.4 wt. %, preferably 5.1 to 5.3 wt. %, based on a total weight of thetreated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of SO₃ of 0.2 to 0.5 wt. %, preferably 0.25 to 0.45 wt. %,preferably 0.3 to 0.4 wt. %, preferably 0.31 to 0.38 wt. %, preferably0.32 to 0.34 wt. %, based on a total weight of the treated palm oil fuelash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of Na₂O of 0.1 to 0.25 wt. %, preferably 0.13 to 0.23 wt. %,preferably 0.15 to 0.22 wt. %, preferably 0.17 to 0.21 wt. %, preferably0.18 to 0.2 wt. %, based on a total weight of the treated palm oil fuelash.

In some embodiments, the treated palm oil fuel ash has a weightpercentage of P₂O₃ of 1 to 5 wt. %, preferably 2 to 4 wt. %, preferably3 to 3.8 wt. %, preferably 3.2 to 3.6 wt. %, preferably 3.3 to 3.5 wt.%, based on a total weight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash of the presentdisclosure has a loss on ignition (LOI) of less than 4 wt. %, preferablyless than 3 wt. %, preferably less than 2.5 wt. %, preferably less than2.4 wt. %, preferably less than or equal to 2.3 wt. %, based on a totalweight of the treated palm oil fuel ash.

In preferred embodiments, the treated palm oil fuel ash comprises, asconstituent oxides, 66 to 68 wt. % SiO₂, 6 to 7 wt. % Al₂O₃, 5 to 6.5wt. % Fe₂O₃, 5 to 6 wt. % CaO, 2.5 to 3.5 wt. % MgO, 4.5 to 6 wt. % K₂O,0.3 to 0.35 wt. % SO₃, 0.18 to 0.2 wt. % Na₂O, and 3 to 4 wt. % of P₂O₃,each based on a total weight of the treated palm oil fuel ash.

In some embodiments, the treated palm oil fuel ash has a median particlesize (d₅₀) of 0.5 to 2.0 μm, preferably 0.6 to 1.8 μm, preferably 0.7 to1.6 μm, preferably 0.8 to 1.4 μm, preferably 0.9 to 1.2 μm, preferably1.0 to 1.1 μm, preferably 1.068 μm.

In some embodiments, the treated palm oil fuel ash has a specificsurface area of 1.4 to 1.6 m²/g, preferably 1.45 to 1.58 m²/g,preferably 1.5 to 1.56 m²/g, preferably 1.51 to 1.54 m²/g, preferably1.52 to 1.53 m²/g.

The treated palm oil fuel ash may be used as a partial replacement ofcement or may be used in combination with one or more other binders(discussed below) in a binder blend. Therefore, in such circumstances,the treated palm oil fuel ash may be employed in an amount of up to 30wt. %, preferably up to 25 wt. %, preferably up to 20 wt. %, preferablyup to 15 wt. %, preferably up to 10 wt. %, preferably up to 5 wt. %,preferably up to 1 wt. %, preferably up to 0.5 wt. %, based on a totalweight of the concrete composition. However, the treated palm oil fuelash may be advantageously employed as a complete cement replacement, andwherein the TPOFA is the only binder present. Thus, in preferredembodiments, the treated palm oil fuel ash is the only binder present,and is employed an amount of 20 to 30 wt. %, preferably 21 to 29 wt. %,preferably 22 to 28 wt. %, preferably 23 to 27 wt. %, preferably 24 to26 wt. %, preferably 25 wt. %, based on a total weight of the concretecomposition.

In the present disclosure, other binders which may be optionallyincluded in the concrete composition, but which are preferably excludedfrom the concrete composition, include any cement and/or pozzolan/burnedorganic matter residues (other than TPOFA) capable of producingcement-like binding properties.

Exemplary cements may be any hydraulic cement or a non-hydraulic cement,for example, Ordinary Portland Cement (OPC) type I, type II, type III,type IV, type V, type Ia, type IIa, type IIIa or a combination thereof(in accordance with the ASTM CI50 standard); Portland fly ash cement;Portland Pozzolan cement; Portland silica fume cement; masonry cements;EMC cements; stuccos; plastic cements; expansive cements; white blendedcements; Pozzolan-lime cements; slag cements; slag-lime cements;supersulfated cements; calcium aluminate cements; calcium sulfoaluminatecements; geopolymer cements; Rosendale cements; polymer cement mortar;lime mortar; Pozzolana mortar; and the like, as well as mixturesthereof.

Exemplary pozzolanic and/or burned organic matter residues may include,but are not limited to, limestone; fly ash (e.g. siliceous fly ashand/or calcareous fly ash), for example Class C fly ash, Class F flyash, pulverized fly ash, ultrafine Class F fly ash; slag; ground blastfurnace slag (GGBFS or GGBS); cement kiln dust (CKD); silica fume orother fine forms of silica such as fine silica flour; metakaolin;vitreous calcium aluminosilicate (VCAS); carbon nanofibers and othercarbon products; calcium hydroxide (Ca(OH)₂); date palm ash or simply“palm ash”, which is produced as wastage during the production of palmfirewood and coal products (typically has a chemical constitution of30-40 wt. % SiO₂, 0.1-1.0 wt. % of Fe₂O₃, 10-15 wt. % of CaO, 0.1-1.0wt. % of Al₂O₃, 5-10 wt. % of MgO, 2-10 wt. % of K₂O, and 1-5 wt. % ofNa₂O); burned palm oil products (other than palm oil fuel ash) such asoil palm shell (OPS); rice husk ash; volcanic ashes and pumices (e.g.,crushed volcanic glass); diatomaceous earth; synthetic pozzolans such assynthesized reactive aluminosilicate glasses; zeolite materials such ascalcined zeolites; cenospheres; pozzolana; calcined shale; trass;pumice; siliceous clays; metropolitan waste ash; sewerage ash; coal washtailings; mineral tailings; scoria; obsidian; other flue ashes; andother ash derived from burning organic waste.

Aggregate

The concrete composition of the present disclosure includes one or morecoarse aggregates. Coarse aggregates are used to influence theconcrete's freshly mixed and hardened properties, mixture proportions,and economy of producing. The types and amounts of coarse aggregate canbe varied depending on the application. For example, the type and amountof coarse aggregate can be varied to produce a lightweight concrete witha bulk density commonly less than about 1450 kg/m³, a normal weightconcrete with a bulk density of about 1500 to 2400 kg/m³ (ASTM C33), ora heavyweight concrete with a bulk density of greater than 2400 kg/m³(ASTM C637 and C638).

Exemplary coarse aggregates include, but are not limited to, crushedrecycled concrete, crushed stone, gravel, rocks, natural soil, quarriedcrushed mineral aggregates from igneous (granite, syenite, diorite,gabbro peridotite pegmatite, volcanic glass, felsite, basalt),metamorphic (marble, metaquartzite, slate, phyllite, schist,amphibolite, hornfels, gneiss, serpentite) or sedimentary rocks(conglomerate, sandstone, claystone, siltstone, argillite, shale,limestone, dolomite, marl, chalk, chert), including unused and wasteaggregates from quarry operations, dredged aggregates, china clay stent,china clay wastes, natural stone, recycled bituminous pavements,recycled concrete pavements, reclaimed road base and subbase materials,crushed bricks, construction and demolition wastes, waste/recycled fluegas ashes, crushed glass, slate waste, waste plastics, egg shells, seashells, barite, limonite, magnetite, ilmenite, hematite, iron, steel,including recycled or scrap steel, and mixtures thereof. In preferredembodiments, the coarse aggregate is crushed stone.

The amount of coarse aggregate deployed herein may vary, but typicalvalues range between but typical values range between 12 to 33 wt. %,preferably 14 to 31 wt. %, preferably 16 to 30 wt. %, preferably 18 to29 wt. %, preferably 20 to 28 wt. %, preferably 22 to 27 wt. %,preferably 24 to 26 wt. %, based on a total weight of the concretecomposition.

Typically, the coarse aggregate has particle size of 2 to 20 mm,preferably 2.1 to 18 mm, preferably 2.3 to 16 mm, preferably 2.5 to 14mm, preferably 3 to 12 mm, preferably 4 to 10 mm, preferably 5 to 8 mm,although coarse aggregates with particle sizes above or slightly belowthese values may also function as intended. The grading of coarseaggregate employed herein preferably conforms to the standard ASTMC33/C33M-18, which is incorporated herein by reference in its entirety.

In preferred embodiments, the coarse aggregate utilized in the concretecomposition has a bimodal particle size distribution, preferably abimodal particle size distribution with a first mode particle size of 4to 12.5 mm, preferably 4.25 to 10 mm, preferably 4.5 to 8 mm, preferably4.75 to 6 mm, and second mode particle size of 2 to less than 4 mm,preferably 2.1 to 3.5 mm, preferably 2.2 to 3 mm, preferably 2.3 to 2.8mm, preferably 2.36 to 2.6 mm. In some embodiments, the first modeparticle size is the predominant particle size. In some embodiments, aweight ratio of the first mode particle size to the second mode particlesize is from 1:1 to 5:1, preferably 1.2:1 to 4.5:1, preferably 1.4:1 to4:1, preferably 1.6:1 to 3.5:1, preferably 1.8:1 to 3:1, preferably 2:1to 2.5:1.

In preferred embodiments, the coarse aggregate has a saturated surfacedry (SSD) specific gravity of 2.4 to 2.7, preferably 2.45 to 2.65,preferably 2.5 to 2.6, preferably 2.55 to 2.56. Saturated surface dry(SSD) is defined as the condition of an aggregate in which the surfacesof the particles are “dry” (i.e., surface adsorption would no longertake place), but the inter-particle voids are saturated with water. Inthis condition aggregates will not affect the free water content of acomposite material. That is, SSD specific gravity is the ratio of theweight in air of a unit volume of aggregate, including the weight ofwater within the voids filled to the extent achieved by submerging inwater for approximately 15 hours, and where the excess, free surfacemoisture has been removed so that he surface of the particle isessentially dry, to the weight in air of an equal volume of gas-freedistilled water at the stated temperature, for example, according toAASHTO T 84.

The concrete composition of the present disclosure also includes one ormore fine aggregates. The fine aggregate may include, but is not limitedto, sand (e.g., dune sand), or any of the materials listed for coarseaggregate which have been ground/pulverized into fine particles. In theevent a coarse aggregate and a fine aggregate are used in the concretecomposition that is sourced from the same material, for example, crushedlimestone, then the particle size will dictate whether it is defined ascoarse or fine aggregate. In preferred embodiments, the fine aggregateemployed herein is dune sand. The fine aggregate may have an averageparticle size of 0.3 to less than 2 mm, preferably 0.35 to 1.5 mm,preferably 0.4 to 1.0 mm, preferably 0.45 to 0.9 mm, preferably 0.5 to0.8 mm, preferably 0.6 to 0.7 mm, although fine aggregates with averageparticle sizes slightly above or below these values may also function asintended. The grading of fine aggregate employed herein preferablyconforms to the standard ASTM C 33/C33M-18, which is incorporated hereinby reference in its entirety.

The amount of fine aggregate deployed herein may vary, but typicalvalues range between but typical values range between 8 to 30 wt. %,preferably 9 to 27 wt. %, preferably 10 to 25 wt. %, preferably 11 to 23wt. %, preferably 12 to 20 wt. %, preferably 13 to 18 wt. %, preferably14 to 16 wt. %, based on a total weight of the concrete composition.

In preferred embodiments, the fine aggregate has a fineness modulus of1.8 to 2.1, preferably 1.81 to 2.0, preferably 1.82 to 1.9, preferably1.83 to 1.88, preferably 1.84 to 1.86, preferably 1.85. The Finenessmodulus (FM) is an empirically determined index of the fineness of anaggregate—the higher the FM, the coarser the aggregate. The finenessmodulus is obtained by adding the cumulative percentages by massretained on each of a specified series of sieves and dividing the sum by100. The specified sieves for determining the fineness modulus for fineaggregate are 0.15 mm, 0.3 mm, 0.6 mm, 1.18 mm, 2.36 mm, 4.75 mm, and9.5 mm, for example, according to ASTM C125 and ASTM C33/C33M-18.

In preferred embodiments, the fine aggregate has a saturated surface dry(SSD) specific gravity of 2.5 to 2.7, preferably 2.55 to 2.68,preferably 2.6 to 2.66, preferably 2.61 to 2.64, preferably 2.62.

In some embodiments, a weight ratio of the coarse aggregate to the fineaggregate is 1:1 to 2:1, preferably 1.1:1 to 1.5:1, preferably 1.2:1 to1.3:1. That is, preferably, the coarse aggregate accounts for 50 to 66wt. % of the total aggregate (coarse plus fine aggregate), preferably 52to 60 wt. %, preferably 54 to 56 wt. %, preferably 55 wt. %.

The amount of total aggregate (TA) utilized herein may vary, buttypically a weight ratio of the total aggregate (coarse plus fineaggregate) to the treated palm oil fuel ash ranges from 1:1 to 2:1,preferably 1.2:1 to 1.95:1, preferably 1.4:1 to 1.9:1, preferably 1.6:1to 1.85:1, preferably 1.7:1 to 1.8:1. In some embodiments, the totalaggregate has a fineness modulus of 3.0 to 4.2, preferably 3.2 to 4.1,preferably 3.3 to 4.0, preferably 3.4 to 3.9, preferably 3.5 to 3.8,preferably 3.6 to 3.7.

Alkali Activator

An alkali activator must be included in the concrete composition. Alkaliactivation generally releases reactive species (e.g., CaO) from thebinder, thus increasing the rate of densification and improving themicrostructural strength of the binder, which by extension affects themechanical properties and durability performance of the cured concrete.The alkali activator may be a mixture of an aqueous solution of a metalhydroxide, preferably an alkali metal hydroxide (e.g., sodium hydroxide,potassium hydroxide, etc.), and a metal silicate, preferably an alkalimetal silicate (e.g., sodium silicate, potassium silicate, etc.). Insome embodiments, the alkali activator may be an aqueous solution of ametal hydroxide, preferably an alkali metal hydroxide.

In preferred embodiments, the alkali activator is an aqueous mixture ofsodium hydroxide and sodium silicate. Preferably, the alkali activatorconsists of sodium hydroxide and sodium silicate in water. A weightratio of sodium silicate to sodium hydroxide may generally range from1:1 to 3:1, preferably 1.2:1 to 2.9:1, preferably 1.4:1 to 2.8:1,preferably 1.6:1 to 2.7:1, preferably 1.8:1 to 2.6:1, preferably 2:1 to2.5:1. In some embodiments, the sodium silicate has a silica modulus(SiO₂:Na₂O weight ratio) of 1.5 to 4, preferably 2 to 3.8, preferably2.5 to 3.6, preferably 3 to 3.4, preferably 3.3. In some embodiments,the sodium hydroxide has a specific gravity of 2 to 2.4, preferably 2.05to 2.3, preferably 2.1 to 2.2, preferably 2.13.

In preferred embodiments, the concrete compositions are prepared using aweight ratio of the alkali activator to the treated palm oil fuel ash offrom 0.3:1 to 0.7:1, preferably 0.34:1 to 0.65:1, preferably 0.36:1 to0.6:1, preferably 0.38:1 to 0.55:1, preferably 0.4:1 to 0.5:1.

The way in which the alkali activator is prepared may also impact thefinal properties of the cured concrete. For example, the concentrationof the sodium hydroxide used to prepare the alkali activator has beenfound to impact the compressive strength of the cured concrete.Typically, the sodium hydroxide and sodium silicate are premixed in theform of an aqueous solution, and this aqueous alkali activator solutionis then added to any dry components to form the concrete composition, aswill be discussed hereinafter. In this process, it has been found thatuse of an aqueous solution of sodium hydroxide having a concentration of8 to 14 mol/L, preferably 9 to 13 mol/L, preferably 10 to 12 mol/L,preferably 10 mol/L ultimately provides cured concretes with superiorcompressive strength properties. Without being bound by theory, it isbelieved that such molar concentrations of sodium hydroxide combineswith the sodium silicate in such a way that effects the rate of silicaand alumina release from the palm oil fuel ash material, and theenhanced dissolution produces cured concrete with superior strengthcharacteristics (e.g., compressive strength).

Water

The cement composition also includes water. In some embodiments, theweight ratio of the water to the treated palm oil fuel ash is 0.06 to0.98, preferably 0.1 to 0.9, preferably 0.2 to 0.8, preferably 0.3 to0.7, preferably 0.4 to 0.6, preferably 0.5 to 0.55. In preferredembodiments, the concrete composition contains 2 to 15 wt. %, preferably3 to 14 wt. %, preferably 4 to 13 wt. %, preferably 5 to 12 wt. %,preferably 6 to 11 wt. %, preferably 7 to 10 wt. %, preferably 8 to 9wt. % water, based on a total weight of the concrete composition.However, such ratios and percentages are exemplary of typical values,and a person of ordinary skill can adjust the water content of theconcrete compositions as needed to suit the application or workabilityrequirements, and the water to binder (POFA) weight ratio or waterweight percentages may therefore fall outside of these described ranges.Suitable water sources include fresh water, potable water, and the like,preferably potable water.

Additives

In some embodiments, the concrete compositions optionally include one ormore additives such as a strength enhancer, an accelerator, a retarder,a plasticizer (e.g., a superplasticizer), a pigment, a corrosioninhibitor, a bonding agent, and a reinforcing material includingmixtures thereof. The additional additive(s), when present, may bepresent in an amount up to 5 wt. %, preferably up to 4 wt. %, preferablyup to 3 wt. %, preferably up to 2 wt. %, preferably up to 1 wt. %,preferably up to 0.5 wt. %, preferably up to 0.1 wt. %, preferably up to0.05 wt. %, preferably up to 0.01 wt. %, based on the total weight ofthe concrete composition.

The concrete composition of the present disclosure may optionallyinclude a strength enhancer, preferably an aluminum-containing strengthenhancer. Exemplary strength enhancers include, but are not limited to,aluminum hydroxide (Al(OH)₃), sodium fluoride, potassium fluoride,sodium sulfate, sodium oxalate, an alkali phosphate (e.g., sodiumphosphate) and related compounds, just to name a few. In someembodiments, when employed, a weight ratio of the strength enhancer tothe treated palm oil fuel ash is 0.01:1 to 0.05:1, preferably 0.015:1 to0.04:1, preferably 0.016:1 to 0.03:1, preferably 0.018:1 to 0.025:1,preferably 0.02:1.

An accelerator is any chemical capable of accelerating the hardening(early strength development) of concrete. Suitable examples ofaccelerators that may be included in the concrete compositions hereininclude, but are not limited to, calcium nitrite, calcium nitrate,calcium formate, calcium chloride, sodium nitrate, or a combinationthereof.

A retarder is any chemical capable of retarding the hardening (earlystrength development) of concrete. Acceptable examples of retardersinclude, but are not limited to, a borate salt such as of sodiumpentaborate (Na₂B₁₀O₁₆), sodium tetraborate (Na₂B₄O₇) and boric acid(H₃BO₃); an organophosphonate such as sodium or calcium salts ofethylenediaminetetra (methylenephosphonic acid) (EDTMP),hexamethylenediaminetetra (methylenephosphonic acid), anddiethylenetriaminepenta (methylenephosphonic acid); acrylamidecopolymers such as copolymers formed from2-acrylamido-2-methylpropane-3-sulphonic acid (AMPS) and one or moreacrylic acid or non-sulfonated acrylamide monomers; metal sulfates suchas ferrous sulfate; gypsum; sugar; sucrose; sodium gluconate; glucose;citric acid; tartaric acid; and the like; as well as mixtures thereof.

Broadly, a plasticizer is a material that when added to another yields amixture which is easier to handle or has greater utility. Theplasticizer as used herein means an organic compound which is usuallynon-volatile at standard room temperature and pressure (25° C., 1 atm.)and which has no specific chemical reactivity. As such, the plasticizeris generally inert towards the binder and merely serves as a medium inwhich that binder may be suspended or otherwise dispersed. Suitableplasticizers may include, but are not limited to, polyalkyleneglycolsand other polyethers such as polyethylene glycol, polypropylene glycol,and polybutyleneglycol, including blends of two or more of suchpolyalkyleneglycols or blends of one or more of such polyalkyleneglycolswith one or more co-plasticizers, as well as phosphonic acid terminatedpolyalkylene glycols; sulfonated or phosphorylated organic compoundssuch as alkyl sulfonic acid esters of phenol and cresol (for exampleMESAMOLL from Lanxess) and aromatic sulfonamides; alkyl or aryl estersof organic acids such as benzoic acid esters of glycols and theiroligomers, esters of 1,2-dicarboxycyclohexane (hydrogenated phthalates),phthalic acid esters, terephthalic acid esters, trimellitates, adipicacid esters, sebasic acid esters, tartrate esters, citric acid estersand sucrose esters; oils which can be natural or synthetic, such asvegetable oils and their derivatives including fatty acid esters andepoxidized vegetable oils, organic liquids derived from wood and otherforest products like liquid rosin esters, hydrocarbon fluids such asmineral oil or paraffinic liquids, and silicones; vinyl polymers such aspolyisobutene, liquid polybutadiene, and polycarboxylates such aspolycarboxylate ethers (PCE) made from polymers of acrylic acid and/ormaleic acid with ether side chains, for example ETHACRYL products fromArkema or MASTERGLENIUM products from BASF; polyesters; formaldehyde(formalin) resins (condensates) such as sulfonated naphthaleneformaldehyde resin, sulfonated melamine formaldehyde resin, acetoneformaldehyde resin, e.g., crosslinked PMS (polymelamine sulfonate) andcrosslinked PNS (polynaphthalene sulfonate); and mixtures thereof.

One particular type of plasticizer known as a superplasticizer (SP) maybe optionally employed in the disclosed concrete compositions.Superplasticizers are also known as high range water reducers, and areadditives generally used in making high strength mortar or concrete. Inpreferred embodiments, when present, the superplasticizer satisfies theASTM C494/C494M-17 requirements, which is incorporated herein byreference in its entirety. The superplasticizers that may be employed inthe present disclosure include, but are not limited to, polyalkylarylsulfonate superplasticizers, such as condensation products ofnaphthalene sulfonic acid with formalin or a salt thereof, acondensation product of methylnaphthalene sulfonic acid with formalin ora salt thereof, and a condensation product of anthracene sulfonic acidwith formalin or a salt thereof, for example, MIGHTY 100, MIGHTY 150,and MIGHTY 200 each available from KAO Corporation, and PANTARHIT FT-500available from Ha—Be Betonchemie; melamine/formalin resin sulfonatesuperplasticizers, for example MELMENT F-10 available from BASF;sulfonated copolymer superplasticizers such as styrene-α-methylstyrenecopolymers containing a mole ratio of from 90:10 to 10:90, preferably30:70 to 70:30, of styrene to α-methylstyrene; polycarboxylates, inparticular polycarboxylate ethers such as those made fromcopolymerization of (meth)acrylic acids, maleic anhydride, maleic acidsor their salts, with polyoxyethylene (meth)acrylic esters or adducts ofpolyethylene derivatives to vinyl monomers, for example MELFLUX orMASTERGLENIUM products available from BASF; or any other plasticizersexhibiting strong tackiness and non-bleeding properties; includingmixtures thereof. In some embodiments, when present, thesuperplasticizer is a chloride-free superplasticizer. In preferredembodiments, when present, the superplasticizer is a sulfonatednaphthalene formalin resin.

Pigments may be optionally included in the concrete composition toeventually form colored cured concretes. Exemplary pigments include, butare not limited to, iron oxide, natural burnt umber, carbon black,chromium oxide, ultra-marine blue, titanium dioxide, among many otherpigments known to those of ordinary skill in the art to provideconcretes with desirable colors.

The concrete compositions may optionally be formulated with corrosioninhibitors. Any corrosion inhibitor known to those of ordinary skill inthe art for use in mortar/concrete applications may be used herein, withspecific mention being made to nitrites (e.g. calcium nitrite),chromates, phosphates, benzotriazoles, alkanolamines (e.g.N,N-diethyl-ethanolamine, N-methyl-ethanolamine, monoethanloamine,diethanloamine, triethanloamine), including mixtures thereof.

Bonding agents may also be optionally included in the concretecompositions. Exemplary bonding agents include, but are not limited to,aluminum sulfate, latex resins such as acrylic polymer latex resins,epoxy resins, vinyl polymer resins, and mixtures thereof.

The concrete composition may also optionally be formulated to include atleast one reinforcing material. The reinforcing materials may provideincreased strength and impact resistance by increasing the flexural andtensile strength of the cured concrete formed from the concretecomposition and thus increasing the amount of energy required to causerupture and complete failure. Exemplary reinforcing materials include,but are not limited to, steel rebar, wire mesh, steel fibers, andsynthetic polymer fibers such as polypropylene fibers, nylon fibers, andpolyvinyl alcohol (PVA) fibers.

In some embodiments, the concrete composition is substantially free ofadditives. In some embodiments, the concrete composition issubstantially free of strength enhancers (e.g., aluminum hydroxide). Insome embodiments, the concrete composition is substantially free ofplasticizers, in particular, superplasticizers. In some embodiments, theconcrete composition is substantially free of organosilicon compounds.In some embodiments, the concrete compositions are substantially free ofsynthetic polymers such as polyvinyl alcohol (PVA), including PVAfibers, either coated or uncoated. In some embodiments, the concretecomposition is substantially free of foaming agents. In someembodiments, the concrete composition is substantially free ofdefoamers. In preferred embodiments, the concrete composition consistsof the treated palm oil fuel ash, the coarse aggregate, the fineaggregate, sodium hydroxide, sodium silicate, and water.

In some embodiments, the concrete composition has a workable flow,expressed as a percentage increase in the average base diameter of a 50mm cube concrete specimen after performing table drops compared to theoriginal base diameter, of 105 to 140%, preferably 110 to 135%,preferably 115 to 130%, preferably 120 to 125%, per ASTM C1437, which isincorporated herein by reference in its entirety.

Any method known by those of ordinary skill in the art may be used tomake the concrete composition of the present disclosure. One exemplarymethod will now be briefly described.

The concrete compositions of the present disclosure may be prepared byfirst dry-mixing the binder (e.g. treated palm oil fuel ash), the fineaggregate, and any solid optional additives either by hand or using amechanical mixer such as a Hobart planetary bench mixer for any timeperiod suitable for removing air pockets and forming a uniform mixtureof dry materials (dry mix). Typical mixing times may be around 0.5 to 10minutes, preferably 1 to 5 minutes, preferably 2 to 3 minutes. In someembodiments, such a dry mix may be obtained as a pre-formed and/orpre-packaged dry mix. The coarse aggregate may be added along with theother components that make up the dry mix or may be combined with analready formed dry mix, and evenly distributed throughout.

Next, the alkali activator (e.g., an aqueous mixture of sodium hydroxideand sodium silicate) may be added and the mixture may be mixed for 1 to10 minutes, preferably 3 to 8 minutes, preferably 5 to 6 minutes,although time periods outside of these ranges may also be acceptable.

In some embodiments, all of the water used to make the concretecomposition comes from the addition of the alkali activator.Alternatively, in some instances it may be desirable to add additionalwater and/or any optional additive(s) (e.g., superplasticizer) afteralkali activation to improve the consistency/workable flow of theconcrete composition or to otherwise change the properties of theconcrete composition/cured concrete. When additional water and/oroptional additive(s) are added, the mixture may be preferably mixed foran additional 1 to 10 minutes, preferably 3 to 8 minutes, preferably 4to 5 minutes, or otherwise to provide an overall average mixing time of8 to 16 minutes, preferably 10 to 14 minutes, preferably 12 minutes.Intermittently, the mixing operation may be stopped to remove any clumpsof solid materials that stick to the bottom of the mixing vessel, andthen mixing may be again continued until a desirable homogeneity andconsistency of the concrete composition has been achieved.

Of course, the relative amounts of the components may be adjusted at anypoint to achieve concrete compositions having the desired properties.For example, the workable flow may be tested according to ASTM C1437 andthe relative amounts of any component(s) (e.g., water, coarse aggregate,fine aggregate, binder, and/or any optional additive(s)) may be adjustedas needed to be within desired specifications.

Cured Concrete

After forming the concrete composition, the concrete composition may bemolded (and demolded), casted, placed, applied, compacted, and/orfinished, and cured (set) as needed to suit a particular application.For example, the concrete composition may be fed into a mold, demoldedand cured, to create any desired shape, for example the shape of amasonry block for application in construction materials. The concretecomposition may be cast in a mold off-site and cured to produce aprecast or the concrete compositions may be cast in a mold or into asite-specific form on-site and cured. The concrete composition may bemolded, casted, placed, applied, and then optionally vibrated in afilled mold or site-specific form to remove air and/or minimizesegregation. In some embodiments, a top surface of the filled mold isremoved and fresh mixture is added to fill the mold. Such vibrationand/or filling steps may be repeated as necessary to produce the desiredcomposition or product. Any molding, casting, placing, applying,compacting, finishing, and/or curing steps may be carried out in acontrolled environment off-site, for example when forming a precast, orperformed on site in standard concrete processes.

Curing may be carried out under ambient conditions, for example 20 to35° C., preferably 23 to 30° C., preferably 25 to 28° C., or throughapplied heat, for example at temperatures of 50 to 70° C., preferably 55to 65° C., preferably 60° C. The cure times may vary from 1 day to 180days, for example, 1, 3, 7, 14, 28, 90, 180 days and any time in betweenthose stated values, preferably 7 to 28 days.

In some embodiments, the cured concrete has a unit weight of 2200 to2300 kg/m³, preferably 2210 to 2290 kg/m³, preferably 2220 to 2280kg/m³, preferably 2230 to 2270 kg/m³, preferably 2240 to 2260 kg/m³,preferably 2250 kg/m³.

The concrete composition described herein provides cured concrete withhigh compressive strength especially considering that cement ispreferably fully replaced with a waste product (i.e., treated palm oilfuel ash). The concrete composition provides, after curing/setting, acured concrete with a 28-day compressive strength of 33 to 49 MPa,preferably 34 to 48.5 MPa, preferably 35 to 48 MPa, preferably 36 to47.5 MPa, preferably 37 to 47 MPa, preferably 38 to 46.5 MPa, preferably39 to 46 MPa, preferably 40 to 45.5 MPa, preferably 41 to 45 MPa. Allcompressive strength tests may be tested using 50 mm concrete samplesaccording to ASTM C39, which is incorporated herein by reference in itsentirety.

The disclosed concrete compositions may be useful in many structural andinfrastructural applications that utilize concrete, brick, or otherstructural element as building material, and in the manufacture ofvarious end use articles or products. In some embodiments, various curedconcrete products are formed from setting/curing the disclosed concretecompositions. The disclosed cured concrete products may be in the formof a useful shape, formed by a variety of means such as, for example,using molds, casts, or forms, or the like, in accord with their intendeduse. Any typical process of forming concrete can be used herein.Therefore, the cured concrete may refer to a molded article or buildingmaterial. For example, the cured concrete may be applied to or otherwiseused to form, slabs, panels, precast panels, wall boards, hollow blocks,floor and roof tiles, catch basins, manholes, beams, columns, posts,conduits and pipes, gravestones, insulators, external cladding, slate,concrete decking, e.g. swimming pools, surfaces and surrounds, ceramicstyle products, marble like products, sink tops, bar tops, bathroomtops, table tops, fireplace tiles, fire proof walls, building blocks(e.g. masonry blocks); both reinforced and not reinforced by steel,depending on the use and purpose for which the manufactured products arefabricated. In some embodiments, the cured concrete described hereinpossess sufficient mechanical properties for use in applicationsdescribed in ASTM C139, which is incorporated herein by reference in itsentirety.

The cured concrete may be optionally reinforced as needed depending onthe application. There are various ways of making reinforced concrete.Reinforced concrete can be made by forming the concrete inside a metalor timber framework or by casting the concrete composition around ridgedsteel bars, or rebars (reinforcing bars) and then cured. Anothervariation called stressed or pre-stressed concrete involves molding theconcrete composition (wet) around pre-tensioned steel wires. The wirescompress the concrete as it sets, making it much harder.

Having generally described this disclosure, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

The present disclosure also contemplates other embodiments “comprising”,“consisting of” and “consisting essentially of”, the embodiments orelements presented herein, whether explicitly set forth or not.

As used herein, the words “a” and “an” and the like carry the meaning of“one or more.”

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

All patents and other references mentioned above are incorporated infull herein by this reference, the same as if set forth at length.

EXAMPLES

Materials and Methods

Palm Oil Fuel Ash (POFA)

POFA was the only aluminosilicate source material and was obtained fromUnited Palm Oil Mill Sdn. Bhd. in Nibong Tebal, Penang, Malaysia. It isa by-product from the combustion of empty palm fruit bunches, palmkernel shells and fibers; normally used to heat the boiler forelectrical energy generation in the palm oil mill. FIG. 1 shows atypical dumping site for raw POFA, which is a combination of well-burntashes and partially burnt palm shells and fibers. The raw POFA particlesare predominantly dark in color due to the presence of high carbonamounts from incomplete burning of the residue. To adequately harnessthe inherent benefits of POFA, POFA was treated to remove unwantedresidue following the procedure highlighted in FIG. 2 . This wasachieved by drying the relatively moist raw POFA in an oven at 100±5° C.for 24 hours, as shown in FIG. 3 to remove the moisture and to allow forease of particles movement through the sieves. After drying, the driedPOFA was sieved through a set of sieves (600 μm and 300 μm) to removecoarser and unwanted materials. Subsequently, after sieving, the sievedPOFA was ground by a mechanical ball mill. The mechanical ball millshown in FIG. 4 has an approximately 7 kg-controlled capacity for eachcycle to achieve an efficient grinding of POFA. It holds 150 steel ballsof sizes ranging from 6 mm to 32 mm and rotating at speed of 180 rpm.Grinding was done to decrease the particle size of POFA and to increaseits surface area, which ultimately led to improved pozzolanicreactivity. At this stage, the POFA material is physically processed butnot thermally treated, hence referred to as ground POFA (GPOFA). Toremove unburnt carbon, prevent glassy phase crystallization andagglomeration of particles, the ground POFA was heated at 550° C. in agas-powered furnace for 90 min. After this calcination process, there isa change in color from black (ground POFA, FIG. 5 ) to grey (calcinedPOFA, FIG. 6 ) due to the removal of carbon responsible for the blackcolor. To further improve the surface area and specific gravity, thecalcined POFA is ground for another round in the ball mill to providetreated palm oil fuel ash (TPOFA). This is because the particlescharacterized by low specific gravity have had improved fineness andparticle size, hence increased specific gravity. The POFA treatmentprocedure adopted was due to the highest improvement achieved, which wasmeasured by the least amount of unburnt carbon content. The synthesis ofalkali-activation of POFA material will improve because of the carboncontent reduction. The loss on ignition (LOI) values reduced from 26% to2.3% after heat treatment, a sign of low unburned residue in the POFA.The reduction in the LOI value is compensated for by an increase in themass percentages of other oxides.

The particle size distribution of the final stage of preparation of POFAwas determined using Laser Particle Sizer Analysette 22 MicroTec plusparticle size analyzer (PSA). The value of the surface area wasdetermined using Micromeritics ASAP2020 BET using nitrogen gasadsorption. Table 1 shows the oxide compositions and physical propertiesof TPOFA and GPOFA, which were determined using X-ray fluorescence (XRF)technique. With total oxides of silicon, aluminium and iron of 79.07%,the TPOFA complies with the specification of ASTM C618 as class F flyash (ASTM C618, 2012).

TABLE 1 Chemical compositions and physical properties of TPOFA and GPOFAProperty Value Chemical TPOFA GPOFA Silicon dioxide (SiO₂), % 66.9162.74 Aluminum oxide (Al₂O₃), % 6.44 6.32 Ferric oxide (Fe₂O₃), % 5.724.87 Calcium oxide (CaO), % 5.56 4.94 Magnesium oxide (MgO), % 3.13 2.51Sodium oxide (Na₂O), % 0.19 0.15 Potassium oxide (K₂O), % 5.20 4.69Sulfur oxide (SO₃), % 0.33 0.26 Phosphorus (P₂O₃), % 3.41 3.72 LOI, %2.3 10.13 Physical Specific gravity (g/cm³) 2.53 2.87 Median particlesize d₅₀ (μm) 1.068 2.96 Specific surface area (m²/g) 1.521 1.683Alkaline Activators

A mixed solution of NaOH_((aq)) and Na₂SiO₃ was used as an activator inthe developed alkali-activated concrete (AAC). Sodium hydroxide is cheapmaterial and it is widely available, making it a choice activator in thealkaline activation of the precursor material, in this case POFA.However, the corrosive nature of the highly alkaline alkali hydroxidespresents handling issues. Commercial grade sodium hydroxide pellets with97% purity and specific gravity of 2.13 were used in the preparation ofsodium hydroxide solution. The NaOH_((aq)) solution was prepared bydissolving either the flakes or pellets in water. The mass of NaOHsolids (flakes or pellets or in a solution) varied depending on theconcentration of the solution expressed in terms of desired molarity ofthe solution. For example, 8M NaOH solution was prepared by dissolving319.976 g of NaOH (in flake or pellet form) in one liter of distilledwater.

Sodium silicate (Na₂SiO₃), also known as water glass, was also used incombination with NaOH as an alkali activator. The silica modulus(SiO₂-to-Na₂O (or K₂O) ratio) varies from 1.5 to 4. The hydrates ofNa₂SiO₃ have the formula Na₂SiO₃.nH₂O where n=5, 6, 8, or 9. Availablewater glass has a silica modulus of 3.3 and holds 36-38% solids.

Water

Potable water, whose physiochemical composition shown in Table 2, wasused in the developed alkali-activated concrete (AAC).

TABLE 2 Physicochemical analysis of potable water used in thedevelopment of AAC Parameter Analytical Method Limits* Results ColorSpectrometric 5.0 TCU <1 TCU Turbidity Photometric 5.0 NTU <1 NTU pH @25 deg C. Electrometric 5 to 7 <1 to 7 Chloride Argentometric 250 mg/L<1 mg/L Iron Photometric 1.0 mg/L <0.05 mg/L (Phematroline method)Manganese Photometric 0.4 mg/L <0.01 mg/L (Persulfate method) SulfatePhotometric 250 mg/L <25 mg/L Nitrate Photometric 50 mg/L <1 mg/L(Diazotization) Lead Direct flame 0.01 mg/L <0.007 mg/L Arsenic Hydridegeneration 0.05 mg/L <0.01 mg/L Cadmium Direct flame 0.003 mg/L <0.002mg/L Total Dissolved Gravimetric 500 mg/L <6 mg/L Solids Limits* meansrecommended contaminant levelsAggregate

In the design of an alkali-activated concrete, selection of aggregatesis important as most of the matrix volume is occupied by aggregates. Thegradation of coarse and fine aggregate (CA and FA) is in accordance withthe provisions of ASTM C33/C33M-18 (2018). The FA was dune sand withfineness modulus of 1.85 while total aggregate (TA) had a finenessmodulus of 3.66. The FA/TA ratio was 0.45 while the specific gravitiesof the CA and FA in the saturated and surface dry (SSD) conditions were2.55 and 2.62, respectively.

The coarse aggregate (CA) used for the AAC was crushed stones composedof sizes 4.75 mm and 2.36 mm, which according to ASTM C33 are size No. 4and No. 8, respectively. The ratio between the size No. 4 and No. 8 usedwas 2.

Superplasticizer

A commercially available polycarboxylic ether basedsuperplasticizer(SP), MASTERGLENIUM 51, available from BASF satisfying the ASTMC494/C494M-17 (2017) was used to modify the workability and to achieveadequate rheological properties of the developed alkali-activatedconcrete. It is a chloride-free super plasticizing admixture.

Mixture Proportioning

AAC with composition shown in Table 3 was prepared with 100% TPOFA, asthe binder, with varying coarse aggregate to total aggregate ratios(CA/TA) and fine aggregate to total aggregate ratios (FA/TA) and aconstant TA/POFA ratio of 1.8. The alkaline activators used wereprepared from a mixture of NaOH_((aq)) (NH) and Na₂SiO_(3(aq)) (NS) withactivator's relative proportion—(Na₂SiO_(3(aq))/xM NaOH_((aq)): [x=10,12 and 14 M]) whose ratios were 2.5, 2 and 1, respectively. The NaOHpellets were measured before dissolution and placed in a beakerdepending on the required molarity; distilled water was then added andthoroughly mixed. For instance, 10 M NaOH_((aq)) is prepared bymeasuring 399.97 g of NaOH pellets into a beaker and distilled wateradded to the 1000 ml mark on the beaker. The solution, which isexothermic, is stirred until all the pellets have dissolved and a clearsolution is obtained. After preparation, the solution is allowed to cooldown to prevent the alkaline activation process from thermalinterference from the exothermic NaOH_((aq)) solution. Based on thealkali activator ratio, the Na₂SiO_(3(aq)) solution was added to themeasured NaOH_((aq)) solution and then mixed for several minutes.

TABLE 3 Constituents of the developed AAC. (NS + NH)/ Water MixtureNS/NH POFA TA/POFA FA/TA CA/TA content Molarity = 10M M1 2.5 0.6 1.80.45 0.55 15%  M2 2.5 0.4 1.8 0.45 0.55 10%  M3 2.5 0.5 1.8 0.45 0.5510%  M4 2.5 0.6 1.8 0.45 0.55 5% M5 2.5 0.6 1.8 0.45 0.55 8% M6 2 0.41.8 0.45 0.55 8% M7 2 0.5 1.8 0.45 0.55 5% M8 1 0.4 1.8 0.45 0.55 10% Molarity = 12M M9 2.5 0.4 1.8 0.45 0.55 10%  M10 2.5 0.5 1.8 0.45 0.555% M11 2.5 0.6 1.8 0.45 0.55 5% M12 2 0.4 1.8 0.45 0.55 10%  M13 2 0.51.8 0.45 0.55 5% Molarity = 14M M14 2.5 0.6 1.8 0.45 0.55 5% M15 2.5 0.61.8 0.45 0.55 4% M16 2 0.4 1.8 0.45 0.55 11%  M17 2 0.5 1.8 0.45 0.5510%  M18 2 0.6 1.8 0.45 0.55 5% M19 1 0.5 1.8 0.45 0.55 10%  M20 1 0.61.8 0.45 0.55 2% M21 1 0.6 1.8 0.45 0.55 5%Concrete Mixing Procedure

An approximate unit weight of between 2200-2300 kg/m³ for the POFAalkali activated concrete is quite comparable to that of typicalPortland cement concrete. In the preparation for the POFAalkali-activated concrete matrix, POFA and aggregates (fine and coarseaggregates) were mixed thoroughly in dry condition using a Hobartplanetary bench mixer model N50-60 to get a uniform mixture of drymaterials. Subsequently, the alkaline activators (a mixture ofNa₂SiO_(3(aq)) and NaOH_((aq))) were added to the dry materials, mixedfor 5 mins and then followed by the addition of water and/orsuperplasticizer (SP), after which mixing was continued for another 4-5mins. Intermittently, the mixer was stopped to scrap manually the solidmaterials sticking to the bottom of the bowl. The mixing continued andstopped when homogeneity and consistency of the concrete mixture havebeen reached after 1-2 minutes.

Casting and Curing of Concrete Specimens

Different specimen specifications and dimensions were used to test thespecimens for compressive, tensile, and flexural strength. For thecompressive strength, the mixtures were cast in two layers into 50 mm×50mm×50 mm oil smeared steel molds. Each layer was compacted on avibrating table for 1-2 mins after which the fresh POFA alkali-activatedconcrete (POFA-engineered cementitious composite (EACC)) samples werecovered in vinyl bags to prevent moisture loss and left in thelaboratory at 25° C. for 24 hours prior to demolding. The specimens weredemolded and placed in vinyl plastic bags prior to curing in an oven at60±5° C. for 24 h. This was to aid in the alkaline activation reactionfor early strength increase. After the heat curing, the hardened sampleswere subsequently allowed to cool down in the laboratory untilpredetermined ages for the test. The same procedures were adopted toevaluate tensile and flexural strength specimens.

Test Methods

The optimized POFA alkali-activated concrete specimens were prepared andevaluated to determine the following properties according to standardprocedures at appropriate curing periods.

-   -   i) In accordance with ASTM C1437, the fresh properties (workable        flow) of the POFA alkali-activated concrete was determined using        a flow table test on 50 mm cube specimens of the POFA        alkali-activated concrete.    -   ii) In accordance to ASTM C39, the compressive strength of 50 mm        POFA alkali-activated concrete cube specimens after 7 and 28        days of curing was measured.        Results and Discussion        Fresh Properties of POFA Alkali-Activated Concrete

The fresh properties of the POFA alkali-activated concrete wasdetermined in order to study the effects of water and the commercialsuperplasticizer (SP) to guide the choice of water or SP in otherexperimental mixtures. The workable flow spread of concrete was in therange of 110-135±5% for both water and SP, so water was selected due tocost. In addition, the spread values qualify the mixtures for hardenedproperties evaluation.

Compressive Strength of POFA Alkali-Activated Concrete

The compressive strength of AAC specimens was conducted at threedifferent ages, 3, 14 and 28 days for showing the influence of mixtureproportions on the strength development with time (Table 4). In general,for the developed POFA alkali-activated concrete herein, the 28-daycompressive strength ranged of 33 MPa to 49 MPa. The compressivestrength property was very much dependent on the sodium hydroxideconcentration, sodium silicate to sodium hydroxide ratio, alkaliactivator/POFA ratio, FA/POFA, CA/POFA and the chemical properties ofPOFA as a binder. It was also seen that the compressive strengthincreased with an increase in the quantity of POFA, a trend that wasevident for all the three ages studied.

TABLE 4 Compressive strength (3, 14, and 28 day, MPa) of the developedPOFA-based alkali activated concrete (NS + NH)/ S/No NS/NH POFA TA/POFAFA/TA CA/TA 3 days 14 days 28 days Molarity = 10M M1 2.5 0.6 1.8 0.450.55 32.15 32.87 35.71 M2 2.5 0.4 1.8 0.45 0.55 46.94 47.94 48.88 M3 2.50.5 1.8 0.45 0.55 37.36 38.30 38.74 M4 2.5 0.6 1.8 0.45 0.55 35.68 35.8436.72 M5 2.5 0.6 1.8 0.45 0.55 36.98 37.34 37.94 M6 2 0.4 1.8 0.45 0.5531.58 32.46 37.68 M7 2 0.5 1.8 0.45 0.55 33.42 33.48 33.92 M8 1 0.4 1.80.45 0.55 19.30 27.06 33.38 Molarity = 12M M9 2.5 0.4 1.8 0.45 0.5537.84 39.10 44.58 M10 2.5 0.5 1.8 0.45 0.55 43.14 43.70 44.14 M11 2.50.6 1.8 0.45 0.55 36.80 37.38 38.94 M12 2 0.4 1.8 0.45 0.55 35.84 38.3639.38 M13 2 0.5 1.8 0.45 0.55 36.30 38.08 38.50 Molarity = 14M M14 2.50.6 1.8 0.45 0.55 25.58 36.26 36.64 M15 2.5 0.6 1.8 0.45 0.55 29.6630.32 36.64 M16 2 0.4 1.8 0.45 0.55 25.89 30.72 34.66 M17 2 0.5 1.8 0.450.55 31.44 37.04 37.70 M18 2 0.6 1.8 0.45 0.55 32.18 36.62 37.98 M19 10.5 1.8 0.45 0.55 28.82 32.78 34.46 M20 1 0.6 1.8 0.45 0.55 33.50 35.2437.14 M21 1 0.6 1.8 0.45 0.55 33.50 38.42 38.82Merits of the Developed Alkali-Activated Concrete

-   -   I. The developed AAC utilizes an agricultural waste material,        palm oil fuel ash, dumped on landfills, as the sole binder.    -   II. With respect to the environment, the palm oil fuel ash        (POFA) alkali-activated concrete is sustainable and eco-friendly        due to the huge availability of POFA.    -   III. With respect to United Nation sustainable development        goals, the use of POFA significantly reduces the carbon        footprint for concrete manufacture because Portland cement is        not used as cementitious binder.    -   IV. The development of the innovative alkali-activated concrete        is cheap in comparison with the cost of OPC concrete, which then        results in substantial savings in the cost of structural and        infrastructural applications.    -   V. The beneficial use of POFA agricultural wastes in the        invention conserves hectares of lands currently used for        landfills, allowing the lands to be used constructively, e.g.,        for the development of roads, buildings etc.    -   VI. The concrete of the present disclosure proved to have        excellent fresh and hardened properties, in some case achieving        a compressive strength of almost 50 MPa, making it suitable for        most structural applications.

The invention claimed is:
 1. Ash-containing concrete composition,comprising: a treated palm oil fuel ash, wherein the treated palm oilfuel ash is the only binder present; a fine aggregate; a coarseaggregate; and an alkali activator comprising an aqueous solution ofsodium hydroxide and sodium silicate, wherein the coarse aggregate has asaturated surface dry (SSD) specific gravity of 2.4 to 2.6.
 2. Theconcrete composition of claim 1, wherein the treated palm oil fuel ashis present in an amount of 20 to 30 wt. %, based on a total weight ofthe concrete composition.
 3. The concrete composition of claim 1,wherein the treated palm oil fuel ash has a median particle size (d₅₀)of 0.5 to 2.0 μm.
 4. The concrete composition of claim 1, wherein aweight ratio of a combined weight of the coarse aggregate and the fineaggregate to the treated palm oil fuel ash is 1:1 to 2:1.
 5. Theconcrete composition of claim 1, wherein a weight ratio of the alkaliactivator to the treated palm oil fuel ash is 0.3:1 to 0.7:1.
 6. Theconcrete composition of claim 1, wherein a weight ratio of sodiumsilicate to sodium hydroxide is 1:1 to 3:1.
 7. The concrete compositionof claim 1, which consists of the treated palm oil fuel ash, the coarseaggregate, the fine aggregate, sodium hydroxide, sodium silicate, andwater.